Role of HRCT Temporal Bone in Predicting Surgical Difficulties Encountered in Fenestral Otosclerosis Surgery

To study spectrum of high resolution computed tomography (HRCT) imaging findings in otosclerosis, to predict approximate length of prosthesis required from pre-operative HRCT measurements and to correlate between oval window niche (OWN) height preoperatively and difficulty in introducing foot plate perforator during surgery. A cross sectional study was conducted on 23 patients with a clinical diagnosis of otosclerosis from September 2018 to July 2020. Sensitivity of HRCT in detecting otosclerosis, correlation between pre-operative incudo-stapedial length (ISL) and intra operative prosthesis length, and correlation between OWN height and difficulty in introducing perforator were sought. The mean age of 23 patients studied was 39.9 years with a female preponderance of 56.5%. 17 out of 19 patients with foci of otosclerosis during surgery had HRCT findings of otosclerosis providing a sensitivity of 89.5%. Mean OWN height obtained was 1.29 mm preoperatively and a cut off value of 1.325 mm found using receiver operating characteristic curve method classifying OWN height as narrow or normal. Mean ISL measured pre operatively was 4.25 mm and mean length of prosthesis used was 4.56 mm with significant positive correlation using intraclass correlation coefficient method with correlation coefficient = 0.879. HRCT is an invaluable modality aiding the surgeon to detect otosclerotic foci with high sensitivity, identify thick obliterative otosclerotic foci requiring additional drilling, to predict the length of prosthesis used and to predict difficulties in approaching footplate when OWN height is below 1.325 mm.